1. Field of the Invention
The present invention relates to a water-based ink. More specifically, the present invention relates to a water-based ink which can be suitably used for printers for inkjet printing, and a process for preparing the water-based ink.
2. Discussion of the Related Art
As coloring materials for water-based inks, aqueous dispersions containing a water-soluble dye or pigment have been used. Since the water-soluble dye has a wide range of color tones and is excellent in color reproducibility, the water-soluble dye has been used as a coloring material suitable for photographic printing. On the other hand, since a pigment-containing aqueous dispersion is excellent in weathering resistance, the pigment-containing aqueous dispersion has been used as a coloring material which is suitable for a long-term storage of printouts and outdoor use.
However, there are some disadvantages in using a water-soluble dye, such that the water-soluble dye is deteriorated in water resistance and light fastness, so that the water-soluble dye is likely to be blotted when printed on plain paper. Also, there are some disadvantages in using a pigment-containing aqueous dispersion, such that the pigment-containing aqueous dispersion has worsened fixing ability on paper surface, and deteriorated water resistance, rubbing resistance and high-lighter fastness when a surfactant or a water-soluble polymer is used as a dispersant in order to improve dispersion stability of the pigment. Furthermore, there is a disadvantage in using a pigment-containing aqueous dispersion, such that the pigment-containing aqueous dispersion is more likely to be blotted when printed on plain paper, although not so worse as the water-soluble dye.
Therefore, recently, there have been proposed a technique of containing a polymer emulsion of a water-insoluble polymer in an ink, and a technique of incorporating a dye or pigment into a polymer emulsion.
For instance, Japanese Patent Laid-Open Nos. Sho 54-058504, Hei 7-258591 and Hei 7-268260 disclose the use of fine polymer particles into which a hydrophobic dye is incorporated in order to improve water resistance. Also, Japanese Patent Laid-Open No. 2000-239591 discloses that a polymeric latex is added to an ink in order to improve rubbing resistance. Furthermore, Japanese Patent Laid-Open Nos. Hei 03-056573 and Hei 03-160069 disclose that fine polymer particles are added to an ink for the purpose of improving blotting resistance and fixing ability.
However, there are some disadvantages in using these techniques such that jetting property when jetted with an inkjet printer is insufficient, so that the printouts are likely to become blurry, even though there are certain effects in water resistance, rubbing resistance and blotting resistance.
Japanese Patent Laid-Open No. 2000-239591 discloses that a specialized solvent is further added to an ink in order to improve its jetting property. However, when this solvent is added to the ink, the desired optical density may not be obtained. Therefore, this process is not necessarily effective from the viewpoint of quality of the printed characters.
Japanese Patent Laid-Open No. Hei 03-56573 discloses that fine polymer particles are cross-linked in order to prevent clogging of the nozzles. However, there are some disadvantages in using this technique, such that and the ink fixing abilities such as rubbing resistance are insufficient, even though the cross-linking degree of the fine polymer particles is increased to a certain extent in order to sufficiently improve clogging of the nozzles.
The present invention relates to a water-based ink which is excellent in high-lighter fastness and rubbing resistance.
The present invention also relates to provide a water-based ink which is excellent in jetting property when printed with an inkjet printer.
These and other advantages of the present invention will be apparent from the following description.